A UMTS wireless access system contains two main network elements: a radio network controller (RNC) and a Node B The RNC and the Node B communicate with each other using an Iub interface. In view of general network establishment mode, the main coverage is implemented in one of following manners: an RNC and an integrated macro cell with multiple sectors, or a RNC together with a distributed base station indoor building baseband unit (BBU) and a macro radio remote unit (RRU). In addition, there are a few femto cells for blind area compensation or hotspot coverage. In conclusion, entire network coverage is implemented by a combination of macro cells and a few femto cells.
With the rapid development of the mobile broadband services in recent years, the enormous applications of data services of various user equipments (UEs) in 3rd generation partnership project (3GPP) mode, such as cell phone, data card, tablet PC, directly lead to an explosive increase of data traffic in hotspot areas (various indoor and outdoor scenes). The data traffic requirement cannot be meet only by improving performance of traditional macro cells. Thus, at present, the dramatically increasing requirement for data traffic is met by using small cells. In terms of power, small cells are classified into micro cell adapted to a power of 2×5 w to 2×10 W, metro cell adapted to a power of 2×1 w, pico cell adapted to a power of 2×250 mw.
Small cells may be applied to outdoor hotspot or hot zone coverage, indoor hotspot or deep hot zone coverage, of which the number would be large, and several times and even tens times with respect to the number of macro cells. The number of metro cells and pico cells with small power is particularly large. If a wide deployment of small cells is still realized in traditional small cell form, the following problems will arise:
1. Each deployment of a small cell requires an engineer to configure a small cell connection on the RNC side, making the network deployment time-consuming and laborious.
2. The continuous increase in capacity of an existing RNC with the increase of deployed small cells makes the cost increased and is disadvantageous to the maintenance and management.
3. The RNC is required to allocate cell resources and processing capability to a small cell, just like those required to be done for a macro cell, though the cell capacity of a small cell is small. For example, for a base station with three sectors each having four carriers, each cell may contain 64 to 96 HSPA+ users on average, and each sector with four carriers contains 256 to 384 (=4*64 to 4*96) HSPA+ users in total, whereas, each cell of a small cell only has 16 to 32 HSPA+ users. In terms of the capacity concerning the number of users, the capacity of a macro cell is 2 to 6 times higher than the capacity of a femto cell.
4. The mobility between small cells leads to the generation of a large number of soft handover signalling on the Iub interface. Furthermore, since small cells and macro cells are logically connected to different RNCs, the handover of a UE between a small cell and a macro cell requires a cross-RNC Iub soft handover signalling, excessive signalling interactions increase the resource consumption and a long handover delay leads to a high call drop rate.